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Study on Resource Recovery by Application of Vacuum Membrane Distillation in Rare Earth Production

Author: TangJianJun
Tutor: ZhouKangGen；MaRongJun
School: Central South University
Course: Metallurgical Separation Science and Engineering
Keywords: Rare earths Hydrochloric acid Sulfuric acid Ammonia Vacuum membrane distillation Diffusion dialysis
CLC: TF845
Type: PhD thesis
Year: 2002
Downloads: 376
Quote: 1
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Abstract

A rare earth smelting process, on the one hand the use of sulfuric acid, hydrochloric acid, and ammonia (or ammonium bicarbonate) and other chemical raw materials, on the other hand, and contains large amounts of sulfuric acid, hydrochloric acid or ammonia which, in the production process, some of the intermediate or the wastewater discharges compounds require processing. Currently, the traditional approach this part of the acid (sulfuric acid, hydrochloric acid) and to meet technical requirements, pH wasted great, and the row of high concentrations of ammonia nitrogen for the production process, because there is not yet economically viable processing by adding alkali generally not added any treatment on the direct emissions of rare earth the smelter surrounding environment can not be ignored. Comprehensive recovery of this part of the sulfuric acid, hydrochloric acid and ammonia compounds and reused in the production process, can undoubtedly reduce raw material consumption of the production process, thereby reducing production costs, improve economic efficiency, and can greatly reduce the amount of inorganic salt or wastewater emissions, its social The effect is self-evident. This article is based on this consideration, first proposed the application of modern new membrane separation technology - vacuum membrane distillation and diffusion dialysis, envisaged in the rare earth smelting process, the purpose is to achieve comprehensive recovery resources of the production process to improve the environment of rare earth smelters status on three typical solution system - rare earth chloride containing hydrochloric acid solution (HCl-RECl ₃-H ₂ O), sulfuric acid containing rare earth sulfate solution ( H ₂ SO ₄-RE ₂ (SO ₄) ₃-H < sub> 2 O) and an aqueous solution containing a high concentration of ammonia nitrogen (NH ₄ Cl or (NH ₄) ₂ SO ₄-H ₂ O) of the membrane recycling system. For rare earth chloride solution, the first study of vacuum membrane distillation recycling including hydrochloric acid, the method can achieve a recovery which high concentrations of hydrochloric acid, a low concentration of the rare earth concentrate. 2 O solution system H ₂ O activity and average HCl ion activity coefficients calculated by of HCl-RECl ₃-H _{of rare earth chloride vapor-liquid equilibrium relationship of the complex solution system thermodynamic analysis results show that the recycling rare earth chloride solution in hydrochloric acid RECl ₃ salting-out effect of vacuum membrane distillation is very favorable; based on AlCl ₃ simulation of rare earth chloride salt, the effects of temperature, solution concentration AlCl ₃ and decompression of the lateral pressure factors on the separation of azeotrope solution system HCl The effects of experimental results and thermodynamic analysis of the results of the same; simulate the stripping liquid typical ingredients in a heavy rare earth rare earth smelters actual experimental results show that the rare earth concentration about 3-fold concentrated hydrochloric acid recovery rate of up to 80% or even more, And because the process of rare earth interception rate of 98% or above in the vacuum side of recovery than pure hydrochloric acid. So far, membrane distillation continuous operation in order to achieve separation of the azeotrope systems also have not been reported, the authors first Membrane continuous rare earth chloride solution was concentrated by distillation under reduced pressure were studied. Experimental results show that as long as the control the circulating fluid ReCl ₃ constant concentration steady state, found that the hydrochloric acid concentration of the circulating fluid, although the feed liquid ReCl _{3 and hydrochloric acid concentration changes, remain unchanged, the greater the concentration of rare earth solid to liquid, the greater the equipment unit membrane area processing capacity corresponding changes in the smaller range of the concentration of hydrochloric acid had no significant effect processing power of the device unit membrane area; addition, solid to liquid ingredients at the same time, the cycle The liquid RECl ₃ The higher the concentration of rare earth concentration factor is greater, the smaller the equipment unit membrane area processing capability, but also will significantly reduce the circulating fluid concentration of hydrochloric acid, the greater the hydrochloric acid recoveries. Consecutive Central South University, Bo on Dissertation Digest enrichment process material balance calculations, and combined with the experimental results made a mathematical simulation of the process by the mathematical model for a certain component of the feed solution, as long as the control of a certain the REC13 concentrated multiples, per unit membrane area determining device processing capability, a hydrochloric acid concentration of the concentrated solution, a hydrochloric acid recovery and recovery liquid hydrochloric acid concentration. For the rare earth solution of low concentration of sulfuric acid, the vacuum membrane distillation a diffusion dialysis joint Membrane recycling wherein sulfuric acid, i.e. the first film distillation under reduced pressure was concentrated rare earth solution of low concentration of sulfuric acid, and then the diffusion dialysis treatment concentrate to achieve the recovery of sulfuric acid. The method provides a clever solution to the problem of the separate diffusion dialysis recycling existing. The system examines the relationship between the side of the pressure and the reduced pressure side temperature vacuum membrane distillation process decompression, first proposed to strengthen the process by reducing the vacuum side temperature and mass transfer; vacuum membrane distillation concentrated sulfuric acid rare earth solution study investigated the composition of the feed solution, the temperature, under reduced pressure side pressure and flow rate and other factors on the water flux; the longer diffusion dialysis for recovering sulfuric acid solution of rare earth sulfuric. The circulation results showed that the dialysis process, the feed solution of sulfuric acid concentration decreasing, while increasing sulfuric acid concentration of the dialysis fluid, and has a high rejection rate of the rare earth diffusion dialysis to achieve the purpose of effective separation of sulfuric acid and rare earth . Once-through results showed that the device units drastically reduced the amount of time to deal with the recoveries greater control recovery was 70 to 80% is appropriate, and the water feed flow ratio greater recoveries bigger, but the sulfuric acid concentration of the dialysate dilution is very obvious, and control flow ratio of water to feed about 1; vacuum membrane distillation first concentrated rare earth solution of low concentration of sulfuric acid, and then the experimental results show that the diffusion dialysis recovered, concentrated by vacuum membrane distillation, diffusion dialysis treatment is greatly reduced, while the dialysis liquid sulfuric acid concentration increased significantly, while the concentration factor is the larger, more obvious effects. So far, reflects the recovery operation parameter quantitative relationship the diffusion dialysis mass transfer mathematical model is still very rarely reported in the literature, the authors derived mass transfer mathematical model of diffusion dialysis. Circulation experimental results, the quantitative relationship between return temperature sulfuric acid diffusion mass transfer coefficient within a certain range; once-experimental results with the calculated results; derivation of the mathematical model to simulate the operating parameters on diffusion dialysis process. The results showed that the mathematical model calculation results agree well with the experimental results, mathematical models can provide guidance on the actual operation. Vacuum membrane distillation process rare earth metallurgy containing high concentrations of ammonia effluent basic research, the method can achieve a high concentration of ammonia nitrogen removal in wastewater back and recycling of ammonia used in the production process. Thermodynamic analysis on the form of distribution of ammonia aqueous systems, the results show that the ammonia nitrogen in the system to maintain the pH of the solution system or more of the value of H is basically in the form of free ammonia; removal of aqueous ammonia and then vacuum membrane distillation study investigated ammonia starting concentrations, the influence of the temperature, the flow rate of the feed solution and decompression-side pressure, and other factors on the deamination and the average water flux; derived deamination process mass transfer coefficient}}

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